A typical self-propelled mechanical street sweeper comprises a cab and a chassis having a sweeper mechanism mounted thereon. The sweeper mechanism generally comprises a pick-up brush mounted at the rear of the chassis a pair of gutter brooms suspended from the sides of the chassis for sweeping debris towards the pick-up brush, a conveyor or elevator for conveying the debris up and away from the pick-up brush, a hopper for storing the debris, and a mechanism for dumping the hopper.
It has been found that unless the pick-up brush is mounted reasonably close to the rear wheels of the sweeper chassis, some of the debris swept towards the pick-up brush by the gutter brushes is left behind on the road as the sweeper turns corners. The reason for this problem is that the swath of the rear pick up brush is not in complete conformity with the path of the vehicle, as the vehicle negotiates corners. This problem can be overcome by mounting the elevator between the rear wheels of the sweeper, and the pick-up brush right behind the rear wheels. However, standard production truck chassis tend to have a through rear axle. Therefore in order to provide sufficient clearance for the elevator, most prior art sweepers are mounted on a custom-made chassis having a pair of stub rear axles. Custom chassis are, however, expensive to build in small volumes. Additionally, most custom chassis sweepers are built for slow speed use only, because of the difficulties associated with certifying a custom chassis for highway speed. As a result, driving such sweepers long distances between jobs tends to be a slow and uncomfortable process.
Attempts have been made in the past to create a sweeper which can be mounted on an OEM or production truck chassis, so as to avoid the need to design and manufacture a custom chassis. One such prior art design includes a trailer for housing the rear pick-up brush which is pulled on casters behind the truck chassis, a reduced-width elevator which fits in between the frame of the chassis, and an auger mechanism for channelling the dirt swept up by the rear brush into the reduced-width elevator. However, because the pick-up brush of this prior art design protrudes too far to the rear, there exists a disconformity between the swath of the sweeper and the path of the vehicle as it turns a corner, resulting in less effective sweeping action than sweepers utilizing custom truck chassis. Also, in the case of this prior art design, there exists the risk that its pick-up brush trailer could be damaged by impact against a curb as the sweeper turns a corner.